Phylogenetic Taxonomy and Classification of the Crinoidea (Echinodermata)
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Journal of Paleontology, 91(4), 2017, p. 829–846 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2016.142 Phylogenetic taxonomy and classification of the Crinoidea (Echinodermata) David F. Wright,1,* William I. Ausich,1 Selina R. Cole,1 Mark E. Peter,1 and Elizabeth C. Rhenberg2 1School of Earth Sciences, 125 South Oval Mall, Ohio State University, Columbus, OH 43210, USA 〈[email protected]〉, 〈[email protected]〉, 〈[email protected]〉, 〈[email protected]〉 2Department of Geology, Earlham College, 801 National Road West, Richmond, IN 47374, USA 〈[email protected]〉 Abstract.—A major goal of biological classification is to provide a system that conveys phylogenetic relationships while facilitating lucid communication among researchers. Phylogenetic taxonomy is a useful framework for defining clades and delineating their taxonomic content according to well-supported phylogenetic hypotheses. The Crinoidea (Echinodermata) is one of the five major clades of living echinoderms and has a rich fossil record spanning nearly a half billion years. Using principles of phylogenetic taxonomy and recent phylogenetic analyses, we provide the first phylogeny-based definition for the Clade Crinoidea and its constituent subclades. A series of stem- and node-based defi- nitions are provided for all major taxa traditionally recognized within the Crinoidea, including the Camerata, Disparida, Hybocrinida, Cladida, Flexibilia, and Articulata. Following recommendations proposed in recent revisions, we recog- nize several new clades, including the Eucamerata Cole 2017, Porocrinoidea Wright 2017, and Eucladida Wright 2017. In addition, recent phylogenetic analyses support the resurrection of two names previously abandoned in the crinoid taxonomic literature: the Pentacrinoidea Jaekel, 1918 and Inadunata Wachsmuth and Springer, 1885. Last, a phyloge- netic perspective is used to inform a comprehensive revision of the traditional rank-based classification. Although an attempt was made to minimize changes to the rank-based system, numerous changes were necessary in some cases to achieve monophyly. These phylogeny-based classifications provide a useful template for paleontologists, biologists, and non-experts alike to better explore evolutionary patterns and processes with fossil and living crinoids. Introduction Given their general significance and broad scientific utility across multiple disciplines of inquiry, it is paramount that the Crinoids are a diverse, long-lived clade of echinoderms with a biological classification of crinoids reflects their evolutionary fossil record spanning nearly half a billion years and are repre- heritage. Numerous emendations and informal suggestions for sented by more than 600 species living in marine ecosystems major taxonomic revisions have been opined over the past today (Hess et al., 1999). The geologic history of crinoids is few decades (e.g., Kelly, 1986; Simms and Sevastopulo, 1993; revealed through a highly complete, well-sampled fossil record Ausich, 1998a, 1998b; Webster and Jell, 1999; Hess and (Foote and Raup, 1996; Foote and Sepkoski, 1999) displaying a Messing, 2011), but the most recent comprehensive revision to complex pageant of evolutionary radiation, extinction, ecologic crinoid classification is the 1978 Treatise on Invertebrate innovation, and morphologic diversification (Ausich and Paleontology (Moore and Teichert, 1978). Since publication of Bottjer, 1982; Ausich et al., 1994; Foote, 1999; Peters and the Treatise, the value of revising rank-based systematic Ausich, 2008; Deline and Ausich, 2011; Gorzelak et al., 2015). classifications to be consistent with phylogenetic hypotheses The spectacular fossil record of crinoids is greatly enriched and and/or the explicit use of phylogenetic taxonomy (sensu de complemented by detailed biologic studies on living species. Quieroz and Gauthier, 1990; Sereno, 1999, 2005) has become These studies facilitate opportunities to synthesize information increasingly common in paleontology (e.g., Smith, 1984, 1994; from fossil and extant forms. For example, comparative studies Holtz, 1996, 1998; Sereno, 1997; Padian et al., 1999; Brochu between fossil and living crinoid species have provided insight and Sumrall, 2001; Carlson, 2001; Carlson and Leighton, 2001; into species ecology and niche dynamics (Meyer and Macurda, Brochu, 2003; Forey et al., 2004; Sereno et al., 2005; Butler 1977; Ausich, 1980; Roux, 1987; Kitazawa et al., 2007; et al., 2008; Kelley et al., 2013). We agree with these authors Baumiller, 2008), established developmental bases for mor- that all named taxa in a biological classification system should phologic homologies (Shibata et al., 2015a), and informed ideally represent clades (i.e., monophyletic groups). The phylogenetic hypotheses (Simms and Sevastopulo, 1993; Rouse development of phylogeny-based classifications is not without et al., 2013). Thus, crinoids form a data-rich model system for difficulties or criticism (e.g., Benton, 2000, 2007). However, we exploring major questions in the history of life. advocate that recent advances in understanding the phylogenetic relationships of major crinoid lineages make the biological classification of the Crinoidea ripe for revision. * Present address: Department of Paleobiology, National Museum of Natural ‘ ’ History, The Smithsonian Institution, P.O. Box 37012, MRC 121, Washington, A great strength of so-called phylogenetic taxonomy is its DC 20013-7012, USA 〈[email protected]〉 potential for increasing nomenclatural stability (de Quieroz and 829 Downloaded from https://www.cambridge.org/core. IP address: 83.84.38.139, on 20 Feb 2021 at 04:48:25, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/jpa.2016.142 830 Journal of Paleontology 91(4):829–846 Gauthier, 1994; Brochu and Sumrall, 2001). Under a of lumping forms together because they are alike in phylogeny-based system of classification, groups of taxa are structure without considering how the likeness arose. organized by their patterns of shared common ancestry rather –F.A. Bather (1898, p. 339) than diagnostic traits. This is a particularly useful aspect of phylogenetic taxonomy: if named evolutionary units are defined Formal scientific description and classification of crinoids began by their history of common ancestry, they do not change if new in 1821 when J.S. Miller recognized fossilized stalked echino- information comes to light that necessitates modification of derms from the “environs of Bristol” as a distinct group. taxonomic diagnoses. For example, new fossil discoveries and/ Although he did not include comatulids in his original concep- or more nuanced understandings of phylogenetic relationships tion of the Crinoidea, he anticipated that they were crinoids: may alter the distribution of synapomorphies among members “The combination of these results with those from the Crinoidea of a clade but do not alter the definition of the clade. Moreover, made me anxious to examine the Comatulae … an animal which by naming taxa on the basis of cladogram topologies, phylo- would be defined with sufficient precision as a Pentacrinus genetic taxonomy can provide a precise definition for groups destitute of the column” (Miller, 1821, p. 127). Further, he previously difficult to diagnose by a unique combination of judged Marsupites ornatus Miller, 1821 (an unstalked crinoid of synapomorphies, such as the Articulata (Simms, 1988; Webster Cretaceous age) to be the ‘link’ between comatulids and his and Jell, 1999; Rouse et al., 2013). To avoid potential instability Crinoidea (Miller, 1821, p. 139). Extant stalked crinoids were in taxonomic nomenclature and/or the proliferation of clade unknown until the mid- to late 1860s, when their discovery names, we advocate that major changes in crinoid systematics during oceanic dredging expeditions provided fodder for early should: (1) be based on well-supported phylogenetic hypotheses debates regarding the efficacy of Darwin’s (1859) then recently inferred using rigorous and repeatable quantitative techniques, proposed theory of natural selection (see Alaniz, 2014; Etter and and (2) employ widely used names and/or names with historical Hess, 2015). Thus, the original description, definition, and precedence if available. diagnosis of the Crinoidea relied entirely on fossil remains. In this paper, we propose a series of stem-based and node- Despite the morphological diversity and deep phylogenetic based clade definitions to help standardize nomenclature for divergences among groups of extant species, the inclusion of crinoid higher taxa. The clade definitions proposed herein are living crinoids with fossil forms has not fundamentally altered informed by a series of recent phylogenetic analyses (Ausich Miller’s (1821) concept. Following subsequent inclusion of et al., 2015; Cole, 2017; Wright, 2017) and represent the first the comatulids and extant stalked crinoids with fossil forms, attempt to classify crinoids using the principles of phylogenetic the Crinoidea has withstood nearly 200 years of scrutiny as a taxonomy (de Queiroz and Gauthier, 1992, 1994). distinct group within the Echinodermata. Although Linnaean classifications lack rigorous criteria for In contrast with their long-term recognition as a clade, the assigning ranks, they can nevertheless provide useful (if coarse) classification of taxa within the Crinoidea has been widely debated reflections of phylogenetic relatedness and divergence among since the nineteenth century (Müller, 1841;